Glass filled polypropylene: PP GF30 and short-glass grades from 10% to 40%

10%, 20%, 30% and 40% glass compared

The values below come from published producer and compounder data sheets for short-glass PP. Stiffness, strength and heat deflection climb with glass level. Notched impact stays low and changes less. Each cell names its test basis: ASTM sheets (D638, D790, D256, D648) and ISO sheets (ISO 527, 178, 179, 75) give different numbers for the same material. Use the table to see the pattern and to sanity-check a data sheet, not to design a part. Unfilled values are from our PP properties page. Every flow value on these sheets is MFR at 230°C / 446°F, 2.16 kg, and the glass grades we read ran about 1–14 g/10 min.

Typical values compiled from individual producer and compounder data sheets for specific grades. The test basis is named in each cell, and rows built on one sheet say so. ASTM D790 (often a 1% secant value) and ISO 178 moduli differ for the same material, grades within one glass level also differ, and notched Izod (J/m) does not convert to notched Charpy (kJ/m²). Compare grades on the same test, and confirm against the data sheet for the exact grade.

Chemically coupled vs. uncoupled

PP is non-polar and does not bond to glass on its own. A coupled grade adds a maleic anhydride grafted PP (PP-g-MA), often about 1–3% of the compound, which reacts with glass sizing made for PP so load passes from the polymer into the fibers. See maleic anhydride grafted polyolefins for how coupling agents are graded.

• What coupling changes. Mainly strength: tensile, flexural strength and fatigue. One compounder's published guidance says 30% chemically coupled glass PP has about 50% higher tensile strength than conventional glass-reinforced grades, without changing modulus, heat resistance or hardness much.
• When uncoupled grades show up. Lower-cost grades where stiffness and flatness matter more than strength, and older grades. They look similar on modulus and HDT, so a buyer comparing only those two lines can miss the difference.
• How to tell. The data sheet often says "chemically coupled" in the description. If it does not, ask. Compare tensile strength against a known coupled grade with the same base and glass level, on the same test.
• Do not mix them up in a qualification. A coupled part that passed a load or snap test can fail with an uncoupled substitute even when the modulus matches. Put "chemically coupled" on the PO.

Homopolymer or copolymer base

Two 30% glass, chemically coupled grades from the same compounder, both tested to ASTM methods, show the trade-off clearly.

One pair of grades from one compounder's data sheets. Other grades vary.

• Homopolymer base is the default for most PP GF30. It gives the highest stiffness and heat deflection at each glass level.
• Copolymer base roughly doubles notched Izod in the pair above, at a cost in stiffness and strength. Some homopolymer grades are also sold impact modified.
• What to send. If you are not sure which base you run, send the data sheet. Modulus and Izod read together often tell a chemist which base it is.

Glass only, or a glass and mineral blend?

Some grades sold under a "GF" or "glass-filled" name are glass and talc or glass and mineral blends. They are real products with a purpose: the mineral evens out shrinkage and cuts warp. But they are less stiff and less strong than straight glass at the same total filler level. One 35% glass/talc grade lists a flexural modulus of about 4.0 GPa by ISO 178, where the coupled 30% straight-glass homopolymer grades we read list about 6.0–6.6 GPa on the same test.

• Write it on the RFQ. "Glass fiber only, no talc or other mineral" if that is what your part was approved on. If you want a blend, give the glass and mineral levels separately.
• Ash is the total, not the type. Ash by ASTM D5630 or ISO 3451-1 gives the total inorganic content. A 30% glass grade and a 20% glass plus 10% talc grade can both ash at about 30%.
• How to check the type. Look at the ash residue: glass leaves fibers, talc leaves a powder. Density helps too. Ask the supplier to state the filler type on the COA or the data sheet, and see glass-filled vs. mineral-filled.
• Calcium carbonate reads low. It breaks down at high furnace temperatures, so agree the ash method and temperature with the supplier.

Warp and fiber orientation

Short glass fibers line up with the melt flow. They restrain shrinkage along the flow and do little across it. Our processing chart lists one 30% glass PP at about 0.24% shrinkage along flow and 1.15% across, about 5 to 1, the largest gap of the filled grades on that chart. Flat and long parts pull out of shape when the two directions differ that much.

• Gate for the long axis. Put the gate where the flow runs along the dimension that must hold, and keep the flow pattern simple.
• Even walls. Uneven walls and unbalanced cooling add to fiber warp. Fix those first. See warped parts.
• Use both shrink values. Tool to the along-flow and across-flow values on the grade sheet, and measure first parts at least 24 hours after molding, 48 hours for polyolefins.
• Options if warp persists. A lower glass level, a glass and talc or glass bead blend, or long glass fiber PP, which often warps less because the long fibers form a network.
• Swapping grades moves dimensions. A different glass level, base resin or coupling package can change shrink. Check first-article dimensions on any substitute.

Recycled-content glass filled PP

Glass filled PP with recycled content is a live product line. One producer's recycled polyolefin family is made with about 25% to 100% recycled resin from PCR and PIR sources, and its published 30% glass grades list about 35% to 65% recycled content, all post-industrial. Before you buy, settle what counts.

• Percent of what? Ask whether the recycled percentage is of the whole compound or of the polymer share. A 30% glass grade at 65% recycled content means nearly all of its polymer is recycled. Virgin glass fiber is not recycled content, so a 30% glass grade cannot be 100% recycled unless the glass is too.
• PCR or PIR. Many brand and customer targets count post-consumer only, and many recycled glass PP grades are built on post-industrial resin. Ask for the split and a third-party recycled-content certificate. See adding recycled content.
• What changes. Recycled PP bases vary more in melt flow, color and odor, and impact can be lower. Many recycled glass grades are black. Ask for COAs from several lots, not one.
• Approvals do not carry over. A UL listing, OEM approval or drinking-water certification belongs to the exact recycled grade. For electrical parts, UL 746S (first published in 2023) covers plastics that contain mechanically recycled material.
• Availability. Some recycled glass PP families are sold only in some regions. Tell us the content you need and we check what our supply partners can quote in the U.S. and Canada.

Where short-glass PP is used

Drinking water. Some glass filled PP grades are certified as materials to NSF/ANSI/CAN 61. A listing covers a specific compound and color, with limits such as water temperature. A data sheet note that a grade is "drinking water acceptable" is not the same as a certification. The finished pump, valve or fitting needs its own certification too, so check the NSF listing for the exact grade before you approve a substitute.

Typical uses only. The part's load, temperature and approvals decide the grade.

Molding notes: drying, temperatures and wear

• Drying. Unfilled PP does not need it, but filled and reinforced PP can pick up surface moisture. Our drying chart gives about 75°C / 167°F for 2 hours when PP needs drying. Some glass PP sheets ask for about 70–80°C / 158–176°F for 2–4 hours. Follow the sheet for your grade.
• Melt and mold temperature. Glass PP sheets we read give melt about 205–260°C / 400–500°F and mold about 27–66°C / 80–150°F. A warmer mold gives a better surface with less glass showing.
• Wear. Glass wears screws, check rings and gates. Hardened or wear-resistant barrels, screws and tool steel last much longer.
• Flow. Check MFR on the COA at 230°C / 446°F, 2.16 kg. Some European sheets give melt volume rate (MVR) in cm³/10 min instead, which is not the same number as MFR in g/10 min.
• Regrind. Regrind shortens glass fibers and lowers strength. Set a limit and test parts at that limit. See regrind limits by resin.

What to put on the RFQ, and how it is priced

Glass filled PP is a compound, so its price does not track the PP index one for one. The base resin, glass fiber, coupling agent, compounding, color and additive packages all sit on top, and recycled-content grades carry their own costs. It often costs less than glass-filled nylon at the same glass level, which is why the swap comes up so often. We do not post prices. We quote a specific grade, quantity, package and ship-to city, through our supply partners and case by case, from one gaylord (about 1,000 to 1,600 lb) to truckloads, and every prime lot from our suppliers ships with a COA.

• The grade you run now, or the drawing callout, such as PP-GF30. Our material code decoder reads those.
• Glass level and tolerance, and "glass fiber only" unless you want a glass and mineral blend.
• Ash on every lot COA, by ASTM D5630 or ISO 3451-1, plus MFR at 230°C / 446°F, 2.16 kg. See what a COA shows.
• Chemically coupled or not, and homopolymer or copolymer base.
• Additive package. Heat-stabilized, UV-stabilized, detergent-resistant, flame-retardant (see flame-retardant PP).
• Color. Black, natural for coloring at the press, or a color match.
• Approvals and documents. OEM spec, UL listing, NSF/ANSI/CAN 61, or an FDA letter if the part touches food.
• Recycled content. The percentage, PCR or PIR, and whether it is a share of the compound or of the polymer.
• Quantity and ship-to. This order, yearly use and the city. Our RFQ package page lists what helps a chemist match a grade.

Common questions

If your grade is not listed, tell us what you run. We source commodity, engineering and specialty resins.